1. Field of the Invention
The present invention relates to directionally solidified multivariant eutectic .gamma.+.beta. nickel-base superalloy articles and compositions, and more particularly to eutectic articles and compositions which include a .gamma. phase nickel-base superalloy matrix reinforced with aligned .beta. phase lamellae, primarily nickel-cobalt-aluminum lamellae wherein the .gamma. phase is a face-centered-cubic solid solution based on nickel and the .beta. phase is a body-centered-cubic (CsCl) ordered intermetallic based on (Ni,Co)Al.
2. Description of the Prior Art
The development of directionally solidifying nickel-base superalloys in the gas turbine engine alloy art has reached the point where current advances are based on identifying eutectic nickel-base superalloy compositions since such compositions permit (a) orientation of eutectic phases and (b) inclusion of eutectic phase reinforcing members such as lamellae.
In directionally solidified eutectic alloy composites, the highly desirable strength properties at high temperatures, i.e. greater than 950.degree. C. (1,742.degree. F.) are provided by metallic composite containing aligned lamellae or fibers as a reinforcing phase dispersed in the alloy matrix. In order to improve the high temperature stress rupture and oxidation properties, it is desirable to identify the alloys, especially oxidation resistant eutectic alloys which can be directionally solidified to provide fiber or platelet reinforced superalloy matrices. Although strong oxidation resistant superalloys involving nickel, aluminum and tungsten, alone or with other alloying additions, are known such as the compositions set out by W. J. Waters and J. C. Freche, Metal Progress (March 1975) pages 57-60, heretofore the identification of oxidation resistant high strength eutectic alloys that can be directionally solidified which contain nickel, tungsten, aluminum and optionally cobalt has not been defined.